1. Field of the Invention
The invention relates to a digital circuit arrangement for influencing the frequency response of a digital audio signal, dependent on the frequency and/or amplitude.
2. Description of the Related Art
Circuit arrangements of this type are particularly required in noise-reduction systems used for reducing the noise produced after a sound carrier has been recorded and subsequently reproduced. Such known systems are, for example the dbx, the HIGHCOM system and the various Dolby systems. In the latter noise-reduction systems, a predetermined filter characteristic is adjusted relative to regards its starting point and the extent of its effect on the audio signal, dependent on the frequency and the amplitude of a signal. Such systems are generally referred to as "Sliding Band Systems".
An encoder which raises, for example, the upper frequency range of the audio signal at the recording end in dependence upon the frequency and/or amplitude of a signal, and a decoder which, in reverse, lowers the same frequency range again at the reproducing end are provided for these noise-reduction systems.
It is known that only analog circuit arrangements are used for most noise-reduction systems of the type described above. The reason is that these circuit arrangements are generally used for analog audio signals only. However, digital apparatuses for reproducing audio signals have increasingly been commercially available in the last few years, which apparatuses should also be capable of reproducing, inter alia, analog audio signals. Hence, it is desirable to provide a digitally operating circuit arrangement which, in conformity with a noise-reduction system, can influence the frequency response of the digital audio signal in dependence upon the frequency and/or amplitude.